1. Technical Field
The present disclosure relates to a method of forming a resist film and, more particularly, to a method of forming an underlayer of a bi-layer resist (BLR) film.
2. Description of the Related Art
As integration of semiconductor devices increases, formation of finer patterns is required. Light having a shorter wavelength is used in photolithography processes to form the finer patterns. For example, as the integration in DRAMs increases to 1 Gbytes, a deep UV region having a wavelength of 193 nm is employed using an argon fluoride (ArF) excimer laser. Accordingly, a resist suitable for the deep UV region is required. A bi-layer resist that provides a large pattern aspect ratio as well as great depth of focus (DOF) margin and high resolution is currently being researched.
The bi-layer resist is composed of a thin toplayer containing Si functionality and a thick underlayer that is under the toplayer. A conventional process of patterning the bi-layer resist includes exposing and developing the toplayer to form the toplayer patterns and thereafter transferring the toplayer patterns to the underlayer using oxygen plasma etch. During the oxygen plasma etch process, the silicon contained in the patterned toplayer reacts to the oxygen, thereby forming silicon oxide. The patterned toplayer containing the silicon oxide acts as an etch mask in the process of transferring a pattern to the underlayer. This process results in a bi-layer having a large thickness, and a toplayer directly exposed to light having a relatively small thickness, which in turn allows for a large aspect ratio and a high resolution.
The toplayer applied in a bi-layer resist has been broadly studied, for example, in SPIE vol. 3999, p. 1171 (2000), SPIE vol. 2724, p. 344 (1996), SPIE vol. 3678 p. 214 (1999), SPIE vol. 3678, p. 420 (1999), J. Photopolym. Sci. Technol. vol. 10, p 585 (1997), but not the underlayer.
The underlayer is required to act as an anti-reflective layer (ARL) in the exposure process of the toplayer. To realize this, it is necessary for the underlayer to have a proper extinction coefficient (k). Secondly, the underlayer is required to have an excellent dry etch resistance during a pattern transfer process to a substrate. Thus, there is a need for an underlayer of a bi-layer resist that is optimized in terms of both extinction coefficient (k) and dry etch resistance.